The present invention relates to drilling apparatus used, for example, in the recovery of petroleum. More specifically the invention relates to a novel system for lubricating the bearings of the cutting rollers of the roller bit in apparatus of this type.
These drilling apparatus typically comprise a plurality of hollow, rotatable tubes referred to as "the drilling string" which at their lower end mount a roller bit body having a number of pivots mounting cutting rollers supported on bearings so as to be freely rotatable about the pivot. The roller bit body usually is provided with nozzles which communicate with an axial passage in the drilling string to allow a supply of mud to be fed to the drilling area.
In the operation of the systems, the cutting elements engage the strata at the bottom of the bore hole to crush or comminute the rock and the mud supplied along the central passage of the drilling string issues out of the roller bit nozzles in the area of the bottom of the bore hole so that the particulate matter set free by the drilling head is washed away and taken along in the return stream of mud ascending through the annular space between the drilling string and the bore hole wall. These systems usually include means for supplying a flushing liquid in the environment surrounding the roller bit to lubricate the same. A system of this type is disclosed in U.S. Pat. No. 2,444,724 to R. W. Brown issued July 6, 1948 and entitled BEARING FOR ROCK BITS. In this arrangement the bearings located in the cutting roller on the side of the roller bearing come in contact with the flushing liquid. It has been observed, however, that this prior arrangement has certain disadvantages and drawbacks. For example, the mud formed during operation together with the abrasion material of the friction bearings or the fatigue scale particles of the roller bearings deposit on the surface of the bearings and there generate increased wear. This produces high operating friction with an unfavorably high operating temperature contributing to rapid bearing wear. Moreover, rapid wear causes large play in the bearing which adversely affects proper guidance of the cutting roller on the pivot of the roller bit. In summary, it has been observed that the service life of bearings lubricated by the prior art systems is accordingly very short.
It is an object of the present invention to provide an improved system for lubricating the bearings of cutting rollers of a roller bit wherein the deposit and accumulation of drilling mud or abrasive filings on the surfaces of the bearings is avoided and at the same time a cooling of the bearing is effected. A further object of the invention is also to provide a system which is comparatively simple in construction and economical to produce.